Hello, I was reviewing the View Template Library (VTL) - see
http://www.zib.de/weiser/vtl/ ... and have a few questions regarding Views
as applied to STL Maps.
I was also wondering if Boost was planning to eventually provide a VTL-like
framework?
I'm looking for a type of View that provides read-only access to an STL map,
with only const iterators, but also provides limited insertion and removal
access as well (as shown below):
This new limited View-like map will only allow clients to iterate using
const iterators, and also provides only one public insert(const key&) and
one erase(const key&) method.
These insert and erase member functions need to be implemented as "Template
Method Functions", as follows: (see Design Patterns)
* Note: these are shown using the latest SGI STL implementation (i.e., the
_M_t.insert_unique and _M_t.erase calls)
virtual bool preInsert(const value_type&)
{
return true;
}
pair insert(const value_type& x)
{
if(preInsert(x) {
return _M_t.insert_unique(x);
}
return make_pair(end(), false); // make compiler happy
}
virtual bool preErase(const key_type&)
{
return true;
}
size_type erase(const key_type& x)
{
if(preErase(x) {
return _M_t.erase(x);
}
return 0; // make compiler happy
}
The preInsert and preErase methods are virtual Hook Methods, and derived
classes override these to add behavior to the (non-virtual) insert and erase
functions..
Another nice addition to this map view would be a const _Tp&
operator[](const key_type& k) const function, implemented something like
this:
const _Tp& operator[](const key_type& k) const
{
const_iterator i = lower_bound(k);
if(i == end() || key_comp(k, (*i).first)) // if i->first is >= k
throw SearchError(k);
return (*i).second;
}
* Note: this simple implementation assumes that the key can be converted to
a string in the constructor of the SearchError exception object.
I have at least three Manager-like (Mediator) classes that can use this
pattern (i.e., derived from this Map View class) as well as others that need
a vector view with a similar filtered design...
Thanks in advance,
~Matt Verona
Houston, Texas
USA
